Foundation Stability of a Levee

Stability of a levee and its foundation soil during flood is governed by seepage forces. In this study, the seepage forces in the flow domain have been determined using conformal mapping technique. Stability of foundation soil has been studied for a levee with and without cut-off wall on permeable soil of infinite depth. In situ effective normal and shear stresses due to self-weight, additional induced stresses due to levee structure and ponded water on upstream sloping face have been determined by assuming soil to be elastic. Besides, components of seepage stress acting at a point on two orthogonal planes, i.e.,on vertical and horizontal planes, are considered and the Mohr's circle is drawn. Mohr-Coulomb failure envelope is drawn for the foundation soil with known effective cohesion ( c'(1)) and angle of internal friction ( phi'(1)),and then the stability of the foundation soil has been assessed. Probable zone of general shear failure considering seepage flow has been identified. Zones vulnerable to foundation failure for different width of levee and depth of cut- off wall have been computed. The hydraulic unstable zone in downstream side of the levee resembles a log spiral. The provision of cut- off wall restricts the progress of failure zone only in the downstream side; otherwise, the zone of failure will enter the foundation of the levee. The stability of the foundation soil of an existing ring levee along the rivers Ganga, Sone and Punpun, near Patna (India), has been evaluated.